Resonant directional couplers for millimetric wave lengths



P. G. MARIE Sept. 30, 1958 RESONANT DIRECTIONAL COUPLERS FOR MILLIMETERIC WAVE LENGTHS Filed July 18, 1956 5 Sheets-Sheet 1 INVENTOR Pierre 6. Marie Y Q I M cum-r14 7b.

ATTORNEYS P. G. MARIE 2,854,636 RESONANT DIRECTIONAL COUPLERS FOR MILLIMETERIC WAVE LENGTHS 5 Sheets-Sheet 2 INVENT'OR Pierre G. Marie fw, J70

, ATTORNEYS & Q w WM S S M TI EM m m Sept. 30, 1958 Filed July 18, 1956 Sept. 30, 1958 P. ca. MARIE RESONANT DIRECTIONAL COUPLERS FOR MILLIMETERIC WAVE LENGTHS Filed July 18, 1956 5 Sheets-Sheet 3 /m W EMJW ATTORNEYS Sept. so, 1958 P. G. MARIE RESONANT DIRECTIONAL COUPLERS FOR MILLIMETERIC WAVE LENGTHS Filed July 18. 1956 5 Sheets-Sheet 4 INVENTOR Pierre G. Marie P ufilmwmflw ATTORNEYS Sept. 30, 1958 i P. G. MARIE 2,

RESONANT DIRECTIONAL COUPLERS FOR MILLIMETERIC WAVE LENGTHS Filed July 18, 1956 5 Sheets-Sheet 5 INVENTOR Pierre G. Marie PM filwww w ATTORNEYS United States Patent RESONAN T DIRECTIONAL COUPLERS FOR MILLI- METRIC WAVE LEN GTHS Pierre G. Mari, Paris, France Application July 18, 1956, Serial No. 598,561

9 Claims. (Cl. 333-) guide in Which an electromagnetic wave is tobe propa gated over large distances in the TE mode.

In applicants copending application filed June 15, 1956, and entitled Wide Band Resonant Directional Couplers,

there are described directional couplers for joining a rectangular guide to a circular guide in which the waves are to bepropagated in the TE mode. These couplers,

which are appropriate where the circular wave guide is" to be short, are not suitable whenthe circular gu1de is to'haveia long length. In circular guides the TE mode is preferable since it has lower'attenuation than the other modes, and an attenuation which decreases withfre quency.

According to one feature of the directional coupler of the invention, the rectangular guide issuing from the energy source, whether a transmitter or receiver, and the circular guide to which it is to be coupled have their axes parallel along the distance used for coupling purposes. Moreover the two are joined by two resonators of identical dimensions constituted by rectangular guides closed upon themselves. Each of these resonators 'includes two straight portionsand two semicircular portions. These resonators will hereinafter be called annular guides. The straight'portions of each resonator are directionally coupled, one to the rectangular guide and the other to the circular guide. With respect to the lengthwise axes of the rectangular and circular guides, which are parallel, the two resonators are displaced with respect'to each other by a quarter of a guide wave length therein in order to conform to the phase conditions relating to the different modes of wave.

The invention will now be further described in conjunction with the accompanying drawings in which:

Fig. l is a cross sectional view of a coupler according 'to the invention, the section being taken on a plane 1-1 Fig. 2 is a fragmentary sectional view of the coupler .ofFig. 1 taken on the line 22 of Fig. 1;

Fig. 3 is a fragmentary sectional view of the coupler of Fig. 1 taken on the line 33 of Fig. 1;

Fig. 4 isa schematic diagram illustrating in thecoupler of Fig. 1 the relationship of theresonators with respect to the rectangular and circular guides which they couple together;

Fig. 5 is -a-diagrammatic representation of a directional coupler according to the invention including a plurality of pairs of annular resonators connected in parallel;

Fig. 6 is a diagram of a further arrangement of couplers according to the invention all employing a common c1rcular guide, the whole forming arnultichannel filter; and

shown in Fig.

Fig. 7 is a diagram of a tuning device for annular resonators.

The example of the coupler of the invention to be described is made up exclusively of machined elements suitably fastened together as for example by screws. While this form of construction is advantageous in order to achieve thedimensional accuracy necessary for operation in the range of millimetric wave lengths, the invention is not limited thereto.

Apart from the tuning elements, the directional coupler of Figs. 1 -3 comprises five principal parts 1-5 identified in Fig. 1. These parts define and enclose openings or cavities, which form the circular guide section 6, the rectangular guide section 7 and the annular guides 8 and 9. The four guides have dimensions such that they have the same guide wave length.

Between the two members 1 and 2 there is formed a cylindrical opening 6 which constitutes the circular guide'and in which the Waves are propagated in the TE .mode employed for transmission overlong distances.

Adjacent the entering and emergent ends of the coupler, 2 at 15 and 16 for the circular guide 6 themembers 1 and .2 possess mating plane faces 10 and 10' which lie in contact with eachother, stressed together by screws .11 and members 4 and 5 which hold members 1,andI2 together. In Fig. 2 themembers .1 and are shown slightly spaced apart. .Over part of the length, of the plane faces 10 there are provided depressions 12 which, when the members 1 and-.2 are assembled together, define the slots 13'and. 14 shown in Fig. l.

The ends of thecylindrical :opening 6 are threadedat 15 and 16 for accommodation-of the ends of the circular gu de in w i h the energy isnto :betransmitted ,over long distances in the TE mode.

Between the members 1 and 3 there is provided a rectangularopening 7, the walls of which constitute a rectangular guide section connecting with the rectangular guide 17 coupled to the associated apparatus, transmitting or receiving for example. In practice it'is convenient actually to extend this external guide 17 into and solder or weld it to the member 3, asindicated in'Figs. l and 3, the bottom wall of the guide 17 being cut away 7 over the central portion of :the coupler as indicated at The members 1 and 3 .contacteach mating plane surfaces 18 and 18' the .central portion of the .coupler, i.e. on.opposite sides of the portion over which extend the slots 13 and 14. In the central portion of the coupler the adjacentfaces .19 and 19 of members 1 and 3 arespacedapart to define slots 23 and 24 ,as indicated in- Fig. 1. These slots extend other only along on opposite sides of over the-length of guide 17 from which the bottom wall is removed and, preferably .overthe same length as slots' 13 and 14.

The slots 13,.231and 14,24 have lengths equal to several wave lengths and operate to effect directional coupling of therectangular and circular guides .6'and 7 to theannular guides Sand 9. Theseannular resonators are formed one in members 1, 2, 3 and 4 and the other in members 1,2, 3, and 5. For the resonator 8, member 4 includes a channel of rectangular cross section having a depth equal to half the'wide dimension of therectangular guide which,

:being closed on itself, forms the-resonator s. This loopshaped channel has a shape which, as seen in Fig. 4, comprises two parallel straightportions joined by two semi-circular portions. Theaother half of the resonator 8 is of matching shape and is formed by suitable conformation of members 1,2 and 3 near the faces thereof which join with member 4, as indicated in Fig. 1. The construction issuch that whenmembersl, 2,. 3 and .4 are assembledtogether with screwsll slotils communicates with the upper straight portion of resonator 8 while slot 13 communicates with the lower straight portion thereof.

The resonator 9 is similarly formed in members 1, 2, 3 and 5, but displaced lengthwise of the coupler, i. e. of the parallel axes of guides 6 and 7, by a quarter-of a wave length as indicated in Fig. 4. Fig. 4 shows the projection, onto the plane identified by the section lines 2-2 and 3-3 in Fig. l, of the mid-sections of the annular guides 8 and 9. For guide 8 this mid-section appears at the interface between member 4 and members 1, 2 and 3. For guide 9, the mid-section appears at theinterface between member 5 and members 1, 2 and 3. In Fig. 4 the projection for guide 9 is shown in full lines at 21 while the projection for guide 8 is: shown in dashed lines at 26, except that lines 21 and 26 coincide in their straight portions. The slots 13 and 14, which have the same projections on the plane of Fig. 4, are shown together, and similarly in the case of slots 23 and 24. Fig.

4 further shows in light dashed lines the generatrices which constitute the limits of guides 6 and 7.

As indicated in Fig. 4 the two resonators 8 and 9 are displaced by a quarter of a wave length. M M' M M M and M indicate in Fig. 4 the cross sectional locations of the guides at which the complex intensities of the waves are measured. According to a theory developed in detail in applicants publication entitled Theorie et Applications des Biquadriondes a wave of intensity t .crossing the section plane M in guide 7 is divided into two parts. One part is further propagated down the rectangular guide 7, arriving at the section plane M with an intensity r,,. The other part penetrates through theslots 23 and 24 into the upper rectilinear portions of the resinators 8 and 9, the slots 23 and 24 acting as directional couplers. This latter part of the energy is then further propagated across the plane M at the section planes 29 and 30 (Fig. 4). The waves which arrive at sections 29 and 30 are in quadrature since they were excited in phase through the slots 23 and 24 and since the two resonators '8 and 9 are displaced, lengthwise of the parallel axes of guides 6 and 7, by a quarter of a guide wave length, )\,,/4. Let be the total intensity across the plane M at the sections 29 and 30. t,- is a complex number whose modulus is the square root of the total flux of energy crossing the sections 29 and 30, its argument being the average of the phases at these sections.

The waves which have traversed the sections 29 and 30 continue and arrive at the slots 13 and 14 in phase opposition as is desirable for excitation of the TE mode in the circular guide 6. The slots 13 and 14 act as directional couplers, and the energy which arrives from the sections 29 and 30 is shared between the TE wave excited in the circular guide 6 and the waves which continue within the guides 8 and 9, arriving at the plane M of the sections 31 and 32 with an intensity r,.

The intensity r, is expressed as a complex number whose modulus is equal to the square root of the total flux of energy crossing the sections 31 and 32, its argument being the average of the phases at these sections.

Let t be the intensity :of the wave thus propagated across the section 33 at the plane M in the circular guide 6, this intensity being defined in terms of the square root of the flux of energy of that wave.

If in the circular guide there is introduced across the section 34 at the plane M' a wave of intensity r its energy will reinforce the waves of intensity and r In applicants publication already cited applicant has shown that the matrix relation flected intensities of optical waves which exchange energy across a partial reflecting plane having no losses.

Similarly the energy corresponding to a total intensity r for the waves which cross the sections 31 and 32 reinforces the waves of intensity r and Between the total intensities t r t r there exists a matrix relation as follows analogous to that previously given:

through the interferometer whereas the others are reflected. Similarly, in the case of the resonant directional coupler of the present invention, it the energy enters in.

the form of a wave of intensity t the totality of the energy will reappear in the wave of intensity t provided the frequency is close to a frequency of resonance for the resonators 8 and 9. The energy is further propagated in the form of a wave of intensity r if the frequency differs too widely from the resonant frequencies of resonators 8 and 9. The dilferent resonant frequencies of the resonators can be computed by noting that the average length of the annular guide closed on itself must for such resonance be equal to an integral number of wave lengths.

In applicants copending application above identified it is shown that a number of directional resonant couplers can be connected in parallel between the guides in order to obtain an improved filtering eifect. Similarly in the case of the present invention, as schematically indicated in Fig. 5, two pairs of annular resonators 3536 and 3738 couple a rectangular guide 7 to a circular guide 6. The two resonators 35 and 36 are tuned to the same frequency and are displaced by l 4 while the two resonators 37 and 38 are tuned to a different frequency. In this manner it is possible to pass very wide bands of frequency, by interspersing the resonant frequencies f f f,, of the first pair of resonators 35-36 with the resonant frequencies 1' f' 3",, of the second pair of resonators 37-38 and by providing that the widths of the pass bands for tthe successive resonances shall be equal to the spacing of adjacent resonances.

Fig. 6 illustrates schematically three directional couplers 39, 40 and 41 coupled on one side to a common circular guide 42 and on the other side to separate rectangular guides 57, 58 and 59. The pairs of resonators 4344 of the coupler 39, 45-46 of the coupler 40, and 47-48 of the coupler 41 are respectively tuned to 35,100 and 35,200 and 35,300 megacycles and have pass bands of approximately 40 megacycles each. At the end 49 of the guide 42 there enter waves whose frequencies are above 35,000 megacycles. The receivers 50 and 51 are intended to cover the bands 35,080 to 35,120 and 35,180 to 35,220 mc. respectively.

The transmitter 52 radiates waves within the band 35,280 to 35,320 mcs. toward the end 49. Thus there are connected to a common circular guide 42 a number of transmitters and receivers which divide between them a band of wave lengths several thousand megacycles in frequency wide, all of which the circular guide is able to transmit. 53 to 56 indicate suitable dissipative terminations.

In the foregoing it has been assumed that the resonators were tuned in their initial dimensioning. In practice it is necessary to provide for adjustment of such tuning. Fig. 7 shows an arrangement suitable for this purpose. In this figure there is shown at 60 a section of one of the resonators, taken on the plane which includes the median section of the wide sides of the guide. 61 is a metallic or dielectric blade insertable and retractable by means of the screw 62 having a knurled button 63 on the end of it. T

Whereas the invention hasbeen described in terms of preferred embodiments various changes may be made therein. For example while the coupling elements have been described as slots, they may of course take the form of pluralities of aligned apertures.

.gu'ides being displaced one'withrespect'to another lengthwise 'of said rectangular and circular guide sections by substantially a guarter of a guide wave length within 'said loop-shaped guides.

'2. A resonant mode-selective directional coupler for radiation of millimetric wave lengths comprising an input rectangular wave guide section, an output circular wave guide section supported parallel to said rectangular wave guide section and dimensioned to the same cut-ofi. frequency in the TE mode as said rectangular section, and two substantially identical cavity resonators each directionally coupled to both of said wave guide sections, said resonators having the shape of loop-shaped rectangular wave guides closed on themselves, said resonators being dimensioned to the same cut-01f frequency as said rectangular and circular sections, said cavity resonators being displaced with respect to each other lengthwise of said guide sections by substantially a quarter of a guide wave length in said loop-shaped rectangular guides, said resonators being further coupled to said guide sections at the same positions lengthwise of said guide sections.

3. A resonant mode-selective directional coupler comprising a rectangular wave guide section, a circular wave guide section parallel thereto dimensioned to the same cut-off frequency in the TE mode as said rectangular section, two resonant loop-shaped rectangular wave guides, and means directionally coupling each of said loop-shaped guides to said guide sections, said loopshaped guides having the same dimensions and being dimensioned to the same cut-off frequency as said rectangular and circular sections and being separated lengthwise of the axes of said guide sections by substantially a quarter of a guide wave length in said loop-shaped rectangular guides, the loop length of each of said loopshaped guides being substantially an integral number of said guide wave length.

4. A resonant mode-selective directional coupler comprising a rectangular wave guide section, a circular wave guide section parallel thereto dimensioned to the same cut-off frequency in the TE mode as said rectangular section, two resonant loop-shaped rectangular wave guides, and means directionally coupling each of said loop-shaped guides to said guide sections, said loop shaped guides having the same dimensions and being dimensioned to the same cut-oft frequency as said rectangular and circular sections and being separated lengthwise of the axes of said parallel guide sections by substantially an odd multiple of a quarter of a guide wave length for radiation travelling in said loop-shaped guides in the TE mode, the loop length of each of said loopshaped guides being substantially an integral number of said guide wave length.

5. A resonant mode-selective directional coupler adapted to interconnect rectangular and circular wave guides, said coupler comprising sections of rectangular and circular wave guides having their axes parallel to each other, said guide sections being dimensioned to the Same cut-01f frequency in the TE mode as said rectangular'section two rectangularwave guides of the same dimensions closed upon themselves into loop shape to form two resonant cavities, said loop-shaped guidesbeing dimensioned to the same cutoff frequency as said rectangular and circular-guide sections, each of said closed guides including two straight portions joined together by curved portions, means directionally coupling one straightportion of each'of said closed guides to said rectangular guide section, and means directionally coupling the other straight portion of each of said closed guides to said circular guide section, said closed guides being positionally staggered lengthwise of said axes,'by substantially an integral multiple of a quarter of a guide wave length for a wave in said closed. guides.

6. A resonant mode-selective directional coupler comprising rectangular and circular wave guide sections supported parallel to each other with their axesdefining -a plane substantiallyperpendicular to the wide dimension of the rectangular guide section, said sections being dimensioned to the same cut-off frequency in the TE mode as said rectangular section, two resonant closed loop rectangular guides of the same dimensions supported on opposite sides of said plane, said closed guides being dimensioned to the same cut-off frequency as said rectangular and circular guide sections said closed guides being positionally staggered lengthwise of the parallel axes of said guide sections by a quarter of a guide wave length for a wave in said closed guides, said closed guides having a length amounting substantially to an integral multiple of said guide Wave length and including each two straight portions parallel to said axes joined by two semicircular portions, and means directionally coupling the straight portions of each of said closed guides one to said rectangular guide section and the other to said circular guide section, said directional coupling means being substantially equally spaced lengthwise of said axes.

7. A resonant mode-selective directional coupler comprising rectangular and circular wave guide sections sup ported parallel to each other with their axes defining a plane substantially perpendicular to the wide dimension of the rectangular guide section, said circular guide section being dimensioned to the same cut-ofi frequency in the TE mode as said rectangular guide section, two resonant closed loop rectangular guides of the same dimensions, said closed guides having the same cross sectional dimensions as said rectangular guide section and being supported on opposite sides of said plane at equal distances therefrom, said closed guides being positionally staggered lengthwise of the parallel axes of said guide sections by a quarter of a guide wave length for a wave in said rectangular guide section, said closed guides having a length amounting substantially to an integral multiple of said guide wave length and including each two straight portions parallel to said axes joined by two semicircular portions, and means directionally coupling the straight portions of each of said closed guides one to said rectangular guide section and the other to said circular guide section, said directional coupling means being substantially equally spaced lengthwise of said axes and extending over a plurality of said guide wave lengths.

8. A resonant mode-selective directional coupler adapted to connect a rectangular wave guide to a circular wave guide for the propagation of energy in said circular wave guide in the TE mode, said coupler comprising a rectangular wave guide section, a circular wave guide section supported parallel to said rectangular guide section, said circular guide section being dimensioned to the same cut-off frequency in the TE mode as said rectangular guide section, two resonant closed loop rectangular wave guides of the same dimensions, said closed guides being dimensioned to the same cut-off frequency as said rectangular and circular guide sections said closed guides being positionally staggered lengthwise of the parallel axes of said guide sections by a quarter of a guide wave length for a wave in said closed guides, said closed guides having a length amounting substantially to an integral multiple of said guide wave length and including each two straight portions parallel to said axes joined by two semicircular portions, and means directionally coupling the straight portions of each of said closed guides one to said rectangular guide section and the other to said circular guide section, said directional coupling means being substantially equally spaced lengthwise of said axes.

9. A resonant mode-selective directional coupler adapted to interconnect a rectangular input wave guide and an output circular wave guide for the propagation of energy in said circular wave guide in the TE mode, said coupler comprising a rectangular wave guide section adapted to support a wave in the TE mode, a circular wave guide section supported parallel to said rectangular guide section, said circular guide section being dimensioned to the same cut-ofi frequency in the TE mode as said rectangular guide section, two resonant closed loop rectangular wave guides of the same dimensions, said closed loop guides being dimensioned to the same cut-oif frequency as said rectangular and circular guide sections, said closed guides being positionally staggered lengthwise of the parallel axes of said guide sections by a quarter of a guide wave length for a wave in said closed guides, said closed guides having a length amounting substantially to an integral multiple of said guide wave length and including each two straight portions parallel to said axes joined by two semicircular portions, and means directionally coupling the straight portions of each of said closed guides one to said rectangular guide section and the other to said circular guide section, said directional coupling means being substantially equally spaced lengthwise of said axes.

References Cited in the file of this patent UNITED STATES PATENTS 2,643,298 Arnold June 23, 1953 2,728,050 Van de Lindt Dec. 20, 1955 2,730,677 Boissinot Ian. 10, 1956 2,748,350 Miller May 29, 1956 2,762,871 Dicke Sept. 11, 1956 

